Two wavelength ranges, or "windows," have been used for communications over single-mode optical fibers. One window is centered around 1310 nm and the other around 1550 nm. Recently, dense wavelength division multiplexing ("DWDM") techniques have been employed to increase the data carrying capacity of optical fibers. Using this technique, a plurality of tightly-packed optical channels within a single window each carry independent data streams. DWDM systems frequently employ optical amplifiers, which are configured to simultaneously amplify all optical channels. Because all commercial DWDM-capable optical amplifiers operate solely in the 1550 nm window, all DWDM systems have operated there.
Both windows may be useful for DWDM applications, potentially simultaneously on the same fiber. However, there are numerous differences between the two windows that manifest themselves at the system level. In conventional single mode fibers, the attenuation in the 1550 nm window is approximately 0.25 dB/km, while it is approximately 0.4 dB/km in the 1310 window. Chromatic dispersion is near zero in the 1310 nm window, but substantial in the 1550 nm window. In dispersion-shifted fiber, the situation is reversed. Beyond the properties of the fiber itself, optical amplifiers in the 1550 nm window differ substantially from those proposed for the 1310 nm window and in some ways are incompatible.
What is required, therefore, are technologies which enable multiple window transmission on the same fiber. The present invention involves a technique that isolates the 1550 nm and 1310 nm windows at key points in a communication link so that important functions such as optical amplification and dispersion compensation may be performed. This will enable the simultaneous implementation of DWDM at both windows on the same fiber.